What’s that in the sky? Is it a bird? Is it a plane? No, it’s a NOAA weather balloon! Balloons aren’t just for birthday parties; they help scientists learn about weather and climate all over the world.

Every day, NOAA’s National Weather Service launches large hydrogen or helium filled balloons from over 100 sites throughout the United States, the Caribbean, and the Pacific. As these balloons rise through the atmosphere, sensors on a small device, called a radiosonde (rā-dē-ō-ˌsänd), measure profiles of air pressure, temperature, relative humidity and winds from the Earth’s surface up to about 20 miles high in the sky. The sensors are linked to a battery powered radio transmitter, which sends the measurements to a ground-tracking receiver.

When the balloons are first released, they are about 5 feet wide, and they gradually expand as they rise due to the decrease in air pressure. When the balloon it high enough and the pressure low enough, it expands until it bursts. A small, orange colored parachute then slows the descent of the instrument to minimize the danger to anyone or anything on the ground. A typical weather balloon will stay aloft for an excess of two hours and can drift about 180 miles from where it was originally released. If the weather balloon enters a strong jet steam, it can travel at speeds exceeding 250 mph.

The National Weather Service uses the data collected by weather balloons to accurately assess and predict changes in the atmosphere. The data help forecasters identify and warn the public and pilots of severe weather, and helps verify satellite data and input for weather prediction models. NCDC maintains these data in the Center’s weather balloon data archive, and they provide valuable information for weather and climate change research.

Radiosondes and their attached flight equipment are perfectly safe to touch despite their sometimes making strange noises or giving off strange smells. Each radiosonde has its own addressed, postage-paid return mailbag. So, if you find a weather balloon or radiosonde, please return to sender. Returning radiosondes benefits the environment and saves taxpayer dollars by recycling the units for reuse.